My company just put on an event (we're a tech company and wanted to put on a tech event). We reached out to people who might want to be sponsors and received money that way and from ticket sales. How do we recognize this? Would it be a contra-expense to off-set the event cost, or do we have to recognize it as revenue some other way?

You have income from sponsors and sales, and you have expenses for the event.
How you 'cost' it internally is your choice.